Normal neural activity is an intricate balance of electrical and chemical signals which can be disrupted by a variety of insults (genetic, chemical or physical trauma) to the nervous system, causing cognitive, motor and sensory impairments. Similar to the way a cardiac pacemaker or defibrillator corrects heartbeat abnormalities, neuromodulation therapies help to reestablish normal neural balance. In particular instances, neuromodulation therapies utilize medical device technologies to enhance or suppress activity of the nervous system for the treatment of disease. These technologies include implantable as well as non-implantable neuromodulation devices and systems that deliver electrical, chemical or other agents to reversibly modify brain and nerve cell activity. The most common neuromodulation therapy is spinal cord stimulation to treat chronic neuropathic pain. In addition to chronic pain relief, some examples of neuromodulation therapies include deep brain stimulation for essential tremor, Parkinson's disease, dystonia, epilepsy and psychiatric disorders such as depression, obsessive compulsive disorder and Tourette syndrome; sacral nerve stimulation for pelvic disorders and incontinence; vagus nerve stimulation for rheumatoid arthritis; gastric and colonic stimulation for gastrointestinal disorders such as dysmotility or obesity; vagus nerve stimulation for epilepsy, obesity or depression; carotid artery stimulation for hypertension, and spinal cord stimulation for ischemic disorders such as angina and peripheral vascular disease.
Neuromodulation devices and systems tend to have a similar form factor, derived from their predecessors, e.g. the pacemaker or defibrillator. Such neuromodulation devices and systems typically consist of an implant containing electronics connected to leads that deliver electrical pulses to electrodes interfaced with nerves or nerve bundles via an electrode assembly. The electrode assembly may be formed of a conductive material and typically take the form of book electrodes, cuff electrodes, spiral cuff electrodes, epidural electrodes, helical electrodes, probe electrodes, linear electrodes, paddle electrodes, and intraneural electrodes.
Conventional electrode assemblies may be made out of bulk silicone, which is biocompatible and soft enough to mitigate most tissue damage during normal motion of the assembly against its implanted surroundings. However, as a bulk substrate, silicone is not amenable to conventional techniques for circuit metallization (e.g., screen printing or lithography of metal layers), and as such, current silicone-based electrode assemblies are typically manufactured in cut-and-paste assembly-based processes. The cut-and-paste assembly-based processes dramatically limit the design complexity of the electrode assemblies, for example, the number of electrodes that can be included, the number of layers of metallization, and any three-dimensional features that might be desired. Alternatively, thin-film electrode assemblies made out of polyimide based material exist that use similar metallization technologies to flex-printed circuit board (PCB) fabrication. However, the thin-film electrode assemblies are not suitable for prolonged use as the stiffness of the material, even at thicknesses as low as 75 μm, is in general significantly mismatched with the tissue and may cause scarring, blood clots, and other tissue damage. In view of these factors, the present inventors believe it may be desirable to develop neuromodulation devices and systems that are capable of having design complexity possible with the thin-film electrode assemblies, and the desirable mechanical properties of the silicone-based electrode assemblies.